Update minimum R version to 4.1 for testthat compatibility

[Copilot]

Description

testthat ≥ 3.0.0 requires R ≥ 4.1, but DESCRIPTION specified R ≥ 4.0. This caused the versions-matrix action to include R 4.0 in the CI test matrix, leading to incompatible builds.

Updated DESCRIPTION to require R ≥ 4.1. Additionally, fixed .github/versions-matrix.R (a custom script that adds an older R version to the test matrix) to respect the minimum R version from DESCRIPTION, ensuring R 4.0 is excluded from all CI test configurations.

Changes Made

• DESCRIPTION: Changed R (>= 4.0) to R (>= 4.1)
• .gitignore: Added R CMD check artifacts (*.Rcheck, *.tar.gz)
• .github/versions-matrix.R: Added logic to filter out R versions below the minimum specified in DESCRIPTION

Related Issue

fix #208

[!WARNING]

Original prompt

---

This section details on the original issue you should resolve

<filter_complete></filter_complete>

<issue_title>Avoid checking R 4.0 on GHA</issue_title>
<issue_description>testthat needs R 4.1.</issue_description>

Comments on the Issue (you are @copilot in this section)

• Fixes Avoid checking R 4.0 on GHA #208

Original prompt

---

This section details on the original issue you should resolve

<issue_title>Avoid checking R 4.0 on GHA</issue_title>
<issue_description>testthat needs R 4.1.</issue_description>

Comments on the Issue (you are @copilot in this section)

• Fixes Avoid checking R 4.0 on GHA #208

---

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[krlmlr]

@copilot: Also double-check GHA workflows.

[Copilot]

@copilot: Also double-check GHA workflows.

Double-checked GHA workflows. Found that .github/versions-matrix.R was re-adding R 4.0 to the test matrix. Fixed in 5f86451 to respect the minimum R version from DESCRIPTION. R 4.0 is now excluded from all test matrices.